Fifty-three one-sea-winter Atlantic salmon Salmo salar (45-63 cm L T ) were radio-tagged in the Tana fjord, Barents Sea, in 1995. Thirty-seven fish (70%) entered the freshwater zone of the River Tana in an average of 3 days after release in the fjord. The migration speeds in the lowest river section below the first riffle area were significantly higher than in the subsequent river section below the second riffle area. Similarly, the observed time spent in the first riffle area was significantly lower than in the next riffle area. The majority of Atlantic salmon entered the river during the hours of high tide and the subsequent ebb tide. In addition, most river entries were recorded around midnight. No effects of river flow on the river entry or migration speed were detected, but the migration speed of Atlantic salmon in both river sections examined was greater at lower temperatures. Twenty-eight fish (72%) were recaptured in the river, 71% of them with weirs and gillnets, and 29% by rod and line. Over half of the Atlantic salmon (54%) were recaptured within 3 weeks following river entry, and within the first 100 km of the river (56%). The results are discussed in relation to earlier studies on multi-sea-winter Atlantic salmon in the River Tana. # 2004 The Fisheries Society of the British Isles

In this study, 221 two-year-old hatchery-reared salmon, Salmo salar, smolts were tagged with radio transmitters over a period of three consecutive years and released in the river in groups of 20-21 fish in various dates between late April and early June. Tagged smolts were tracked during their downstream migration in the lower 36-km stretch of the regulated River Oulujoki, with the focus on the effects of release date, water temperature and river flow on migration behaviour and survival. The results indicate that release timing and river temperature have profound effects on the initiation of migration, swimming speed and survival of released S. salar smolts. Smolts released early in the spring in cold waters ceased migration after brief downstream movement and were vulnerable to predation, whereas the migration speed and survival rates increased markedly for smolts released later in the spring.

No abstract

The accuracy of underwater snorkel counts of adult Atlantic salmon, Salmo salar L., was analysed in a small tributary of the River Teno before and during the spawning period using two independent verification methods (video counts and radio-tagged fish) with known numbers of fish. The observation efficiency of snorkelling crews was generally high, but that of an inexperienced crew (65-72%) was significantly lower than an experienced crew (81-82%). Habitat type affected the accuracy of snorkelers, especially those of the inexperienced crew. The efficiency of snorkelers was high in pool-type habitats (75-100%) but decreased considerably in faster flowing turbulent habitats (43-82%), where the inexperienced crew provided the lowest estimates. Thus, snorkel counting is a valid method for estimating Atlantic salmon spawning population densities in small rivers with adequate underwater visibility and with a sufficiently experienced snorkelling crew.drift diving, observation efficiency, radio telemetry, stock assessment, underwater techniques.

–  In this paper, we describe a method employing motion‐sensing radio transmitters for recording and identifying behavioural patterns and activity of Atlantic salmon spawning under natural conditions. Simultaneous video monitoring verified recorded activity patterns originating from behaviours such as fighting, nest digging and quivering. The method described here enables more accurate determination of the timing and location of spawning compared to conventional location tracking. Motion‐sensing transmitters can also be applied to monitor other species and types of behaviour, and therefore the use and development of such methods deserves further attention in behavioural studies.